1. Field of the Invention
This invention relates generally to crimpable metal sleeves used to remotely secure sutures, and more particularly to such sleeves made from magnesium and its alloys.
2. Description of Related Art
A surgeon's ability to hand tie a secure knot in a suture is severely compromised in many minimally invasive surgical procedures. When absorbable sutures are preferred at remote tissue sites, it would be a significant advance to be able to readily create a strong, safe, low profile absorbable knot.
Less invasive therapeutic interventions are most beneficial when the desired physiological or surgical outcome can be achieved with the least amount of iatrogenic trauma to the patient. For example, advances in laparoscopic surgery have proven to be advantageous relative to traditional open surgical procedures, which often require large skin incisions and significant tissue manipulation just to view the surgical site. Both the patient and society benefit from effective minimally invasive surgical procedures by demonstrated reductions in patient pain, hospital stays and recovery time, as well as in the related medical costs.
It is well recognized that advances in minimally invasive surgery require advances in the technology available to physicians to enable effective interventions through size limited access sites. With specialized equipment and imaging methods, hemostatic tissue dissections, specimen removal, wound closure, etc. can often be realized with minimal damage or disruption to surrounding tissues. Over the past several decades, improvements to laparoscopes, video imaging equipment, trocar access ports, surgical insufflation and irrigation systems, graspers, scissors, cautery devices and suturing and stapling devices for wound closer have led to improved patient outcomes.
For most surgeons, however, the remote hand tying of knots in suture through small access ports remains a significant challenge. Laparoscopic hand tying of sutures has been compared to trying to tie one's shoes with chopsticks.
There have been many prior art attempts to circumvent the need for the knotting of suture. Such prior art devices have essentially been staples, clips, clamps or other fasteners (U.S. Pat. Nos. 5,041,127; 5,080,663; 5,021,059; 4,841,888; 4,741,330; 4,724,840; 4,705,040; 4,669,473; 4,627,437; 4,448,194; 4,039,078; 4,235,238; 4,006,747; 3,875,648; 5,085,661). However, the devices described in the above listed patents do not provide or anticipate the potential advantages of a safe and effective absorbable Magnesium Knot.
Non-absorbable Titanium Knots® delivered through sterile 5 mm Ti-KNOT® TK laparoscopic devices (LSI SOLUTIONS®, Victor, New York, U.S. Pat. Nos. 5,520,702; 5,643,289; 5,669,917; 6,368,334; 6,641,592; 7,235,086) are a currently well accepted commercial alternative to hand tying remote surgical knots. The Titanium Knot® product is based on a surgical crimping technology that deforms a non-absorbable, malleable hollow titanium tube over suture strands to hold them together.
A very recently published study (Chi T. An Ex-Vivo Evaluation of the Application and Strength of a Novel Laparoscopic Knot Substitute Device. J Endourol 24(1):95-98), compared the suture holding strength of traditional hand tied laparoscopic surgical knots (mean tensile strengths 53.0 N, range 27.0-74.9 N) to four different commercially available “laparoscopic knot substitute devices.” Note these authors failed to include the very strong, low profile Titanium Knot®, which has been commercially available for over a decade.
The knots tested in this paper included the Suturelock®, ANPA, San Mateo, Calif., mean tensile strength 14.7 N; Lapra-Ty* devices, Ethicon Endosurgery, Piscataway, N.J., 6.1 N; Hem-O-Lock clips, Weck Closure Systems, Research Triangle Park, N.C., 5.4 N; and an unspecified titanium clip, 3.0 N. The authors of this paper note that the hand tied knots “had substantially higher tensile strengths than any of the knot substitutes (P<0.001 for all)” they tested. While the knots tested in the above study were less than half the strength of hand tied suture knots and below USP standards for minimal average knot strength, Titanium Knots® tested under these conditions would have yielded knot strengths comparable to those of hand tied knots.
Healing wounds often require foreign materials, such as non-absorbable polymeric suture or stainless steel staples, clips and knots to provide structural integrity during the initial acute phases of healing. However, in many applications, long-term healing is best enabled without permanent residual foreign bodies. Surgeons frequently elect to use absorbable sutures, such as braided sutures made of polyglycolic acid (PGA) or monofilament sutures made of polydioxanone (PDO), to avoid risks of future discomfort, infection or stone formation instigated by the long-term presence of foreign materials. For remote minimally invasive procedures, when hand tying suture is a difficult option, Titanium Knots® are frequently used in association with both non-absorbable and absorbable suture materials.
The suture loops created by hand tying knots in absorbable suture materials simply biodegrade or re-absorb over time along with the rest of the remaining suture material. When used with an absorbable suture, a Titanium Knot® is left permanently near the wound closure site after the suture material has re-absorbed.
In addition to non-bioabsorbable metals for surgical knots, Sauer (U.S. Pat. No. 5,669,917) proposed a knot-securing member fabricated from a bioabsorbable polymer such as a homopolymer, copolymer or a blend obtained from one or more monomers selected from the group consisting of glycolic acid, lactide, lactic acid ρ-dioxanne, E-caprolactone and trimethylene carbide. However, multiple attempts of using such bioabsorbable polymers in this application, they have not proved to be an acceptable option. Lapra-Ty* clips can be made of absorbable polymers, but their bulkiness and inherent weakness raises questions regarding their efficacy in critical wound closure applications. To get the suture holding force strength minimally required by United States Pharmacopeia (USP) standards, remotely deployable polymeric-based absorbable knots are simply too big, bulky, and difficult to deploy to be useful in most surgical applications so far.
Magnesium is a remarkable material in a number of relevant ways. While pure magnesium is quite flammable and too rapidly dissolved in the human body, some magnesium alloys have long been recognized for their potential use for non-permanent surgical applications. E. D. McBride first published a paper in 1938. He postulated the exciting opportunity to use this strong metal for internal fixation of fractured bones; the magnesium implant would absorb over time rather than require explantation (McBride E. Absorbable Metal in Bone Surgery. JAMA 8;111(27):2464-2467). Strogenov in 1972 noted some improvements to magnesium using cadmium for surgical orthopedic application (U.S. Pat. No. 3,687,135). Interest in magnesium's implantation for orthopedic applications has waxed and waned throughout the subsequent decades: currently, there are no known commercially available reabsorbable magnesium orthopedic products anywhere in the world.
First reported in 2003, Heublein suggested employing various magnesium based vascular stents to temporarily hold a vessel open during healing (e.g. for opening coronary arteries). (Heublein B. Biocorrosion of Magnesium Alloys: A New Principle in Cardiovascular Implant Technology? Heart 2003;89(6):651-656). Zartner reported in 2005, the first biodegradable stent in the pulmonary artery of an infant (Zartner P. First Successful Implantation of a Biodegradable Metal Stent into the Left Pulmonary of a Preterm Baby. Catheter Cardiovasc Interv. Dec 2005;66(4):590-594.) In 2006, Erne reported, the clinical trials of bioabsorbable vascular stents (Erne M. The Road to Bioabsorbable Stents: Reaching Clinical Reality? Cardiovasc Intervent Radiol 2006;29:11-16.) To our knowledge again, however, no magnesium-based bioabsorbable stents are currently commercially available.
While the use of magnesium alloys for orthopedic structural implants and bio-absorbable stents has been previously reported by others to hold living tissue together (e.g., fractured bones) or apart (e.g., diseased arterial walls), to our knowledge, until now, no one has suggested the surgical use of magnesium alloys to hold non-native foreign materials (i.e., exogenous materials, not intrinsic to the body) like suture. In addition, for previous magnesium alloy medical applications, while all others have proposed using solid rods, wires and screws, our group is the first to describe the use of hollow magnesium components that are crimped together to hold suture materials. In other words, the use of hollow magnesium alloys to temporarily hold together exogenous materials is a new application not obvious to others over the past seven decades; until now, no one has suggested the use of magnesium for absorbable suture knots.
To be clinically relevant, an absorbable knot must be made of a material that has acceptable biocompatibility and excellent strength profiles over specific time periods. Magnesium is found throughout nature and is considered an essential component of the human body. The therapeutic potential of “Epsom salts” rich in magnesium have been recognized since the 17th century. Magnesium is an alkali earth metal from the second main group of the Periodic Table of Elements. This silvery white metal is the eighth most abundant element comprising 2.7% of the earth's crust and 0.13% of sea water. About 30 grams of magnesium is found in a healthy human, mostly in muscle and bone. The U.S. Government has recommended a regular daily adult allowance of magnesium intake of 420 mg/day for males and 320 mg/day for females.
While the degeneration of magnesium by material corrosion, fatigue, erosion, etc., are affected by body variables like temperature, pH, proteins, fluid flows, etc., magnesium alloy mechanical properties can remain substantially strong enough to hold suture together long enough for many healing requirements. Magnesium has the highest strength to weight ratio of all structural metals. Magnesium is 36% lighter per unit volume than aluminum and 78% lighter than iron, both of which are not considered readily biocompatible. Magnesium (˜1.8 g/cm3) is substantially less dense than titanium materials (4.5-4.7 g/cm3). Magnesium based materials are available in a wide range of mechanical properties. Magnesium can be machined, cast, formed, welded, heat treated and annealed.
Today's most widely produced magnesium alloy grade is ASTM AZ31 B. A common example is AZ31 B-F magnesium alloy, where the last letter designates the “temper,” which here indicates “Fabricated,” contains 3% aluminum and 1% zinc by weight and has a tensile strength of 260.0 MPa. Other preferred magnesium alloys incorporate small percentages of rare earth metals and or zirconium and yttrium. Multiple published reports address biocompatibility and relative strength of AZ31 B and other alloys in orthopedic and cardiac applications (Witte F. In Vivo Corrosion of four Magnesium Alloys and the Associated bone Response. Biomaterials 2005;(26):3557-3563. Yibin R. Preliminary Study of Biodegradation of AZ31 B Magnesium Alloy. Front Mater Sci China 2007; (4):401-404. Liu K. Study on Biocompatibility of AZ31 B Magnesium Alloy in Mice. China Biotech 2008;28(3):63-67. Cui F. Calcium Phosphate Coating on Magnesium Alloy for Modification of Degradation Behavior. Front Mater Sci China 2008;2(2):143-148. YaoHua H. Biocompatibility of Bio-Mg—Zn All Within Bone with Heart, Liver, Kidney and Spleen. Chinese Science Bulletin February 2009;54(3):484-491.)